The superfamily Pleurotamaricea first appeared in the late Cambrian period
(about 500 million years ago) The family Pleurotomariidae didn't appear until
the mid Triassic period (about 200 million years ago) The way the fossil
record shows it, most Pleurotomariidae were shallow warm water dwellers. Also
the eyes on recent species are another key that they were originally in under
1,000 feet of water. No known recent species is found in water under 300 ft
(100 m) (although there are reports of some divers finding them at about 250
but it is very very rare)
        Most Pleurotomariids are quite common in their habitat as I have said before.
However the reason why they are not readily available is because of their
habitat. Most live on steep walls that make it almost impossible to trawl or
dredge without astronomical costs. If one were to fish for these guys (without
using trawl nets or dredges) commercially they would need $15000- 20000 a day
for a mini sub. Most days you will only get about 7-10 specimens. That rounds
out to about $2000 a specimen. Most are a lot less than that. I sincerely
doubt that they will become more affordable because of the extreme
inaccessibility. You can sometimes get non perfect specimens (ones with
cracks, bad coloration, chips,etc) for a lot less than the published prices.
        Most, if not all, of your questions can be answered from the book "The Living
Pleurotomariidae." Just a little suggestion but if I were you I would stop
purchasing shells for a little while in order to save up for the book. After
you have gotten the book, then go back to buying shells. Books are just as, if
not more, important than the shells if you are a shell collector Doing the
work on your own (name, locality and other identifications) in order to keep
your collection the way you want it is very important.. you can't have people
always do the work for you. Besides looking up and studying the shells on your
own is really enjoyable and one of the perks of shell collecting. If you can't
answer a question that you have been working on for a long time, then go for
help. It is much more satisfying when you alone have figured out the answer to
a question that has been plaguing you for a while
 
-Sarah